Hepatitis C virus (HCV) is the major etiologic agent of non-A, non-B hepatitis. Currently, more than 170 million people worldwide are chronically infected with HCV. Persistent HCV infection causes chronic hepatitis that can lead to liver cirrhosis and hepatocellular carcinoma. A limited number of effective therapeutic agents specific to HCV are being currently used, but they are still used by combined administration of interferon used as a conventional standard therapeutic agent. The current standard of care for patients with chronic hepatitis C is pegylated interferon (hereinafter referred to as ‘IFN’) plus the nucleoside analogue ribavirin. However, IFN and ribavirin often lead to various side effects as administered alone or in combination, and the sustained virological response rate of IFN against certain HCV genotypes is less than 50%. Currently, only a few inhibitors of HCV enzymes including nonstructural protein (NS)3/NS4A protease and NS5B RNA-dependent RNA polymerase (RdRp), both of which are essential viral components of RNA replicase, are in clinical tests or have been approved for clinical applications. Development of HCV enzyme-specific therapeutics has been hampered because of rapid emergence of resistant mutants caused by the error-prone nature of the viral RdRp. Thus, in addition to viral enzyme targets, host targets have emerged as attractive options for anti-HCV drug development. RNA interference (RNAi) mediated by small interfering RNA (siRNA) is an effective, specific therapeutic entity to silence viral RNA genes. Several previous reports demonstrated the potential use of synthetic and vector-based siRNAs (short hairpin RNAs; shRNAs) as a therapy for HCV by directing siRNAs against various regions of the HCV genome.
However, besides the absence of improved delivery tools, rapid emergence of resistant mutants is a major obstacle in therapeutic application of siRNAs targeted to the viral genome. Because host target mRNAs have a lower chance of escaping from RNAi silencing, host factors required for HCV replication and propagation may be promising targets for anti-HCV siRNA therapy. We previously showed that HCV NS5B RdRp is phosphorylated by protein kinase C-related kinase 2 (PRK2), a Thr/Ser kinase belonging to the protein kinase C family HCV replication was shown to be positively regulated by PRK2 overexpression and is suppressed by pharmacological inhibition of PRK2 with the PRK2 inhibitors HA1077 and Y27632.
Despite recent progress, systemic delivery has been the major hurdle for development of safe and effective siRNA-based therapeutics. The antiviral efficacy of siRNAs used for silencing of various cellular factors required for HCV replication or propagation has not yet been evaluated in vivo in part due to the lack of efficient liver-targeting, more specifically hepatocyte-targeting, siRNA delivery agents, or possibly due to low stability of siRNAs and/or toxicity induced by silencing of critical host factors.
The present invention has been completed by developing an active PRK2 siRNA and assessing whether the PRK2-silencing siRNA can be used as an additional therapeutic option for HCV.